Image display devices such as liquid crystal displays, organic electroluminescent displays, and plasma displays provide high-definition image quality with low power consumption. Such image display devices are also slim due to the flat screens thereof. These image display devices are being used not only in offices or households but also at sites of various kinds of professional work, such as graphic design and medical care.
In a liquid crystal image display device, the reproducibility of the display image is increased, for example, by measuring light from the back surface of a reflection sheet disposed behind a backlight in an image display unit to control the luminance of the backlight.
Patent Literature 1 discloses that an optical sensor for detecting light of a backlight leaking from a reflection sheet is disposed over the back surface of a liquid crystal display unit (in Claim 1 thereof). It also states that a photodetector includes a cushion member for guiding only light leaking from the reflection sheet to the optical sensor and that the cushion member is a donut cushion and is in close contact with a liquid crystal module to shield light.
Patent Literature 2 discloses that a luminance sensor is mounted on an aperture formed in the back surface of a casing and that a reflection sheet also has an aperture as necessary.
Patent Literature 3 discloses that an optical sensor is mounted over the back surface of a chassis with a base therebetween, that a circular hole having a diameter of 3 mm is formed as a reflection sheet hole in a reflection sheet which lies in front of the optical sensor, and that a circular hole having a diameter of 30 mm or less is formed as a chassis hole in the chassis, which lies in front of the optical sensor.
Patent Literature 4 discloses the following image display device: the image display device includes a reflection sheet disposed on the back surface of a backlight lamp and configured to reflect light emitted from the backlight lamp forward, an optical sensor disposed on the back surface of the reflection sheet and configured to detect light introduced through a first aperture formed in the reflection sheet, and a control unit that controls the luminance of the backlight lamp on the basis of the detection result of light applied to the optical sensor; a sensor holder housing the optical sensor is disposed on the back surface of the reflection sheet; the sensor holder has a second aperture having a smaller area than that of the first aperture in the inner region of the first aperture; the sensor holder also has a reflection part on a surface which is near the reflection sheet adjacent to the second aperture and which is exposed from the first aperture; and light from the backlight lamp is introduced into the optical sensor through the first and second apertures (in Claim 1 thereof).